Brake systems for vehicles rely on a vacuum brake booster connected to the vehicle's intake manifold. The total air flow rate into the intake manifold at engine idle and low load conditions can be difficult to control. A typical response to this situation is to provide a control valve having an expensive electric actuator. The control valve and control system is needed to shut down motive flow during engine low load and idle conditions.
Another response to this situation is to position an aspirator between the vacuum brake booster and the manifold. The aspirator provides a narrow flow introduction gap from the air suction flow to the main flow (the motive flow) that functions at a low vacuum pressure all the way to negative 60 kPa.
Under some engine operation conditions (such as during engine idle), pressure inside the brake boost tank may be higher than intake manifold. The narrow gap of the aspirator prevents a high flow rate from the boost tank to the intake manifold. Accordingly, a separate flow bypass is required to quickly flow air out of brake boost tank to achieve desired performance.
The separate flow bypass required by known brake arrangements introduces an additional component that adds cost to the arrangement. In addition, the requirement for the separate flow bypass introduces another element into the vehicle braking system that is subject to failure. Furthermore, the addition of a separate flow bypass adds an additional challenge to engine compartment packaging.
Thus, known brake systems that include aspirators are subject to improvement. Accordingly, a brake system for use with a vehicle that provides an advantage over known systems remains wanting.